Xiaoqin Niu

Toward a highly hemocompatible membrane for blood purification via a physical blend of miscible comb-like amphiphilic copolymers

Comb-like amphiphilic copolymers (CLACs) consisting of functional chains of poly(vinyl pyrrolidone) and polyethersulfone-based hydrophobic chains were firstly synthesized by reversible addition-fragmentation chain transfer polymerization. The CLAC can be used as an additive to blend with polyethersulfone (PES) at any ratio due to the excellent miscibility, and then a surface segregation layer with permanent hydrophilicity could be obtained. The surfaces of the CLAC modified PES membranes were characterized using X-ray photoelectron spectroscopic analysis, Fourier transform infrared and water contact angle measurements. The surfaces are self-assembled with numerous functional branch-like -PVP chains, which can improve the hemocompatibility. The root-like -PES chains (the hydrophobic part) are embedded in the membranes firmly, which greatly reduces the elution during the membrane preparation procedure and repeated usage, and makes the membranes have a permanent stability. The PES-based hydrophobic chains have the same structure as the membrane bulk material, which makes the miscibility of the additive and the membrane material good to ensure the intrinsic properties of the membrane. The modified membranes showed suppressed platelet adhesion and prolonged blood coagulation time (activated partial thromboplastin time, APTT); thus, the blood compatibility of the membranes was highly improved. The strategy may be extended to synthesize other PES-based functional copolymers and to prepare a modified PES dialysis membrane for blood purification.

Super long-life supercapacitor electrode materials based on hierarchical porous hollow carbon microcapsules

Remarkable supercapacitor electrodes with a high specific supercapacitance and a super long cycle life were achieved by using hierarchical porous hollow carbon microcapsules (HPHCMs) as active materials. HPHCMs were prepared by a facile chemical route based on pyrolysis of a soft sacrificial template involving a non-crosslinked core of poly(styrene-r-methylacrylic acid) and a crosslinked shell of poly(styrene-r-divinylbenzene-r-methylacrylic acid), which were synthesized by using traditional radical polymerization and emulsion polymerization. The results of scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller characterizations revealed that HPHCM possessed the desired pore structure with apparent macro-/meso- and micropores, which not only provided a continuous electron-transfer pathway to ensure good electrical contact, but also facilitated ion transport by shortening diffusion pathways. As electrode materials for supercapacitor, a high specific capacitance of 278.0 F g−1 was obtained at the current density of 5 mA cm−2. Importantly, after 5000 potential cycles in 2 M KOH electrolyte at the discharge current density of 20 mA cm−2, the capacitance actually increased from 125 to 160 F g−1 and then remained 151 F g−1, corresponding to a capacitance retention of 120%, likely due to electrochemical self-activation.

Thermoswitchable Janus Gold Nanoparticles with Stimuli-Responsive Hydrophilic Polymer Brushes

Well-defined thermoswitchable Janus gold nanoparticles with stimuli-responsive hydrophilic polymer brushes were fabricated by combining ligand exchange reactions and the Langmuir technique. Stimuli-responsive polydi(ethylene glycol) methyl ether methacrylate was prepared by addition-fragmentation chain-transfer polymerization. The polymer brushes were then anchored onto the nanoparticle surface by interfacial ligand exchange reactions with hexanethiolate-protected gold nanoparticles, leading to the formation of a hydrophilic (polymer) hemisphere and a hydrophobic (hexanethiolate) one. The resulting Janus nanoparticles showed temperature-switchable wettability, hydrophobicity at high temperatures, and hydrophilicity at low temperatures, due to thermally induced conformational transition of the polymer ligands. The results further highlight the importance of interfacial engineering in the deliberate functionalization of nanoparticle materials.

Bionic design for anticoagulant surface via synthesized biological macromolecules with heparin-like chains

While polyethersulfone (PES) represents outstanding oxidative, thermal and hydrolytic stability as well as good mechanical and film-forming properties, the hemocompatibility of PES membranes must be dramatically enhanced to reduce injections of anticoagulants during hemodialysis. In this study, a series of biological macromolecules with heparin-like chains were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization to design anticoagulant membrane surfaces. When the synthesized copolymers were used as additives to modify the PES membrane using the phase separation method, the functional groups of the copolymers migrated and formed a negatively charged coating on the membrane surface. The modified PES membrane blended with a heparin-like block copolymer showed prolonged blood coagulation time and thereby good hemocompatibility. In addition, the clotting time of the modified membrane was enhanced with increasing amounts of the heparin-like amphiphilic tri-block copolymer. Furthermore, the results of the cell morphology and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay suggest that the cytocompatibility increases due to the addition of heparin-like additives. Thus, the heparin-like surface modification method seemed to be a promising approach for application in the biomedical field.

Bionic design for surface optimization combining hydrophilic and negative charged biological macromolecules

While polyethersulfone (PES) membrane represents a promising option for blood purification, the blood compatibility must be dramatically enhanced to meet todays ever-increasing demands for many emerging application. In this study, we report a bionic design for optimization and development of a modified PES membrane combining hydrophilic and negative charged biological macromolecules on its surface. The hydrophilic and ionic charged biological macromolecules sulfonated poly(styrene)-b-poly(methyl methacrylate)-b-poly-(styrene) (PSSMSS) and poly(vinyl pyrrolidone)-b-poly(methyl methacrylate)-b-poly-(vinyl pyrrolidone) were synthesized via reversible addition-fragmentation chain transfer polymerization and used together to modify PES membranes by blending method. A hydrophilic membrane surface with negative charged surface coating was obtained, imitating the hydrophilic and negatively charged structure feature of heparin. The modified PES membranes showed suppressed platelet adhesion, and a prolonged blood clotting time, and thereby improved blood compatibility. In addition, the blood clotting time of the modified membranes increased with the blended PSSMSS amounts increment, indicating that both the hydrophilic and negative charged groups play important roles in improving the blood compatibility of PES membranes.

A new approach for membrane modification based on electrochemically mediated living polymerization and self-assembly of N-tert-butyl amide- and β-cyclodextrin-involved macromolecules for blood purification

We report a convenient, highly efficient, and universal approach for blood-compatible modification of polymer membrane based on the SI-eATRP, RAFT, and self-assembly of N-tert-butyl amide and β-cyclodextrin existed in macromolecules chains. The functional membrane surfaces with any polymer chains of hydrophilic, ionic polymer, and polysaccharide segments, for example, the copolymers of N-vinyl pyrrolidone, sodium p-styrenesulfonate hydrate, and glucose allyl amide, are easily designed and fabricated; and the thickness of polymer brushes are efficiently controlled by polymerization conditions like monomer concentration and initiator amount. As a key bio-plastic, the modified polyethersulfone membrane shows suppressed platelet adhesion, significant decreases in thrombin-antithrombin generation, and the complement activations on C3a and C5a levels compared with pristine polyethersulfone membrane; while the platelet activation (PF4) decreased. Due to the similar groups as heparin-like structure, the modified membrane effectively prolonged the activated partial thromboplastin time, thrombin time, and prothrombin time. The water contact angle of the modified membrane decreases from 89.2 to 22.3°, and the cytocompatibility of the modified membranes largely enhanced. It could be concluded that the new approach could be widely used for polymer membrane modification, and the mimic heparin-like surface seems to be a promising structure to improve the biocompatibility for blood purification application.

A flexible membrane electrode with an electrolyte-affinity surface for energy storage: effects of amphiphilic block copolymers and membrane thickness

We fabricate a porous and flexible membrane electrode composed of nano-nickel hydroxide as an electrochemically active material, a polymer as a substrate material, and a copolymer as a modification additive. A series of amphiphilic block copolymers of PAA-b-PAN-b-PAA, F127, PDMC-b-PAN-b-PDMC, and PVP-b-PAN-b-PVP are prepared, and their effects on the thickness, surface structure, and electrochemical performance of the electrode materials are investigated. It is discovered that the hydrophilic chains of the amphiphilic block copolymer contribute a lot to improving the surface properties of electrolyte-affinity. The results indicate that the electrode membrane with a membrane thickness of 60 μm modified by PAA-b-PAN-b-PAA demonstrates the highest specific capacitance of 3090.0 F g−1 at a current density of 0.5 A g−1. An asymmetric supercapacitor based on the fabricated electrode membrane using Ni(OH)2 as the positive active material and activated carbon as the negative electrode obtains a capacitance of 114.1 F g−1 at 0.5 A g−1. The device shows good cycling stability with a capacitance retention of up to 90.7% after 5000 cycles at 1.0 A g−1. The maximum energy density of the asymmetrical supercapacitor reached 40.6 W h kg−1 at a power density of 400.0 W kg−1, and a high power density of 4000.0 W kg−1 was obtained at 23.5 W h kg−1 in 6 M KOH aqueous electrolyte.